1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording and, more particularly, to a magnetic head structure having a thin magnetic film with improved characteristics.
2. Description of the Prior Art
A large variety of types of magnetic head for perpendicular magnetic recording have heretofore been proposed.
One type of conventional magnetic head for perpendicular magnetic recording will first be described with reference to FIGS. 3, 4 and 5.
As shown in FIG. 3, a magnetic medium 3 which is constituted by a base film 1 and a magnetic film 2 is contacted by a magnetic head which is brought into contact with one side thereof. The magnetic head is arranged such that an electromagnetic coil 4 is disposed in a groove 9 in a core 5 which is formed with a central leg 5a and two side legs 5b and 5c and thus assumes a substantially W-shaped form in cross-section, and a substrate 6 which is constituted by a non-magnetic material is secured to the upper surface of the core 5 in such a manner that a thin magnetic film 7 is vertically disposed on the central leg 5a.
The following is a description of a method of manufacturing a magnetic head arranged as above. Namely, as shown in FIGS. 4(a) to 4(c), a thin magnetic film 7 which is constituted by a permalloy film, a cobalt-zirconium amorphous film or the like is formed by means of evaporation, sputtering, plating or the like on one side surface of a flat plate material 10 which is made of a non-magnetic material having wear resistance, such as a composite material of a ceramic, glass or carbon material and a metallic material and which constitutes the above-described substrate 6 (FIG. 4(b)). Then, the flat plate material 10 having the thin magnetic film 7 formed thereon is subjected to annealing. Thereafter, another flat plate material 14 which has the same quality and the same configuration as those of the above-described flat plate material 10 is bonded to the thin magnetic film 7 by means of glass or an adhesive (FIG. 4(c)).
On the other hand, grooves are cut in the upper surface of a core material 8 which is constituted by a square rod member of a soft-magnetic material, e.g., ferrite, sendust or laminated permalloy in a form such as that shown in FIG. 5(a) and in such a manner that the core material 8 has a substantially W-shaped cross-section, whereby a central leg 5a and two side legs 5b are formed with grooves 9 provided on both sides of the central leg 5a. Then, the core material 8 may be sliced into any desired width (FIG. 5(b)). After slicing, an electromagnetic coil 4 is disposed in the grooves 9 (FIG. 5(c)).
With the core 5 thus formed, the substrate 6 which has been formed as described above and sliced in conformity with the core 5 is bonded to the upper surface of the core 5 by means of glass or an adhesive. By this bonding, the thin magnetic film 7 which is located in the approximate center of the substrate 6 of a non-magnetic material is disposed on the central leg 5a of the core 5. Finally, polishing is carried out in such a manner that curved surfaces are formed on both sides of the substrate 6 as shown by the broken line in FIG. 5(d).
Incidentally, in forming a magnetic head which utilizes a thin magnetic film, the substrate 6 which retains the thin magnetic film 7 is required to possess a relatively low degree of surface roughness. This is because the magnetic properties of the thin magnetic film are affected by the degree of surface roughness of the substrate. In other words, as the thickness of the thin magnetic film decreases, the effect of the surface roughness of the substrate becomes more apparent.
In view of the above-described fact, it is general practice to employ a substrate made of a material which has a low degree of surface roughness, such as silicon or glass. However, such a material is not satisfactory in terms of wear resistance.
Wear resistance becomes an important factor particularly when a metallized tape or the like is employed as the recording medium.
For this reason, there has been an increasing tendency to employ as a substrate material one which has excellent wear resistance, such as carbon or a carbon-based material, e.g., a carbon-based composite material, or a ceramic-based material. However, since these materials are formed by sintering or other similar method, they undesirably have a large number of pores and it is unfavorably easy for them to be worn in small areas during the surface polishing, which fact disadvantageously makes it very difficult to form a flat surface.
In order to solve this problem, a magnetic head has been proposed which has a structure wherein a polymer film having heat resistance, such as a polyimide resin, is formed on the surface of a substrate made of a material such as mentioned above, and a thin magnetic film is sandwiched through this polymer film.
Such a magnetic head, however, involves the disadvantage that the magnetic properties of the thin magnetic film are deteriorated when forming the thin magnetic film on the polymer film by means, for example, of sputtering, this being due to the difference in terms of the coefficient of thermal expansion as between the polymer film material and the thin magnetic film material. More specifically, as a thin magnetic film material, Co-based alloys such as a cobalt-zirconium-niobium (Co-Zr-Nb) alloy may be employed. These alloys have a coefficient of thermal expansion of 100 to 110.times.10.sup.-7 (cm/cm/.degree. C.), whereas polyimide resins have a relatively large coefficient of thermal expansion, such as, 400 to 800.times.10.sup.-7 (cm/cm/.degree. C.) Accordingly, when the polymer film is cooled down from a high temperature to an ordinary temperature when forming the thin magnetic film by sputtering or other similar means, a relatively large contraction of the polymer film causes an internal stress in the thin magnetic film, resulting disadvantageously in deterioration of the magnetic properties of the thin magnetic film.